Optimization of the bi-functional oxygen electrode (BOE) structure for application in a Zn-air accumulator

A novel structure of a bi-functional oxygen electrode (BOE) was developed, which is based on a new technological process of teflonization. The electrochemical oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) were studied in a half-cell configuration, to investigate its charge/discharge characteristics. Both the gas-diffusion layer (GDL) and active layers (AL) of the electrodes were optimized. Preliminary studies of GDLs with different carbon blacks and for different ratios between the PTFE and carbon blacks have shown, that the most stable GDL is produced from Vulcan XC-72 teflonized with 60 % PTFE – TV-60. The innovation regarding the GDL is in the way it is prepared using high-energy mixing, which assures an equal dispersion and intimate contact between the carbon black and Teflon particles. With this GDL an optimization of the AL was performed with respect to both the thickness (amount of catalytic mass – catalyst + PTFE) and the ratio between the catalyst and the binding agent (PTFE). The volt-ampere characteristics and the charge/discharge tests showed that the most suitable catalyst with respect to the stability of the GDE is a mix of Ag and Co3O4. The GDE with the above composition reaches more than 700 cycles without a decrease in performance.